A stratified scavenging two-stroke internal combustion engine includes a mixture passage for supplying air-fuel mixture to a crank case, and an air passage for supplying scavenging air to a scavenging passage. A carburetor is provided in the mixture passage, a throttle valve is provided in the carburetor. In the air passage, an air valve is provided. Conventionally, a rotary carburetor is known in which the throttle valve and the air valve are integrated with the carburetor, as shown in the Patent Documents 1 and 2, for example. Each of the rotary carburetors described in the Patent Documents 1 and 2 includes a body, and a valve element which is rotatably contained in the body, and is configured so that when the valve element is rotated, a mixture passage and an air passage provided in the body, and a mixture passage and an air passage provided in the valve element are communicated or blocked off, namely, the throttle valve and the air valve are opened or closed.
In the Patent Document 1, a two-bore type rotary carburetor is described, in which two bores consisting of a mixture bore with a circular cross section and an air bore with a circular cross section are provided. In the Patent Document 2, a one-bore type rotary carburetor is described in which two passages consisting of a mixture passage with a semi-circular cross section and an air passage with a semi-circular cross section are provided, and the two passages are appeared to form one bore by partitioning them with a plate-like partition.